1. Field of the Invention
The invention relates to a hybrid vehicle and in particular to a hybrid vehicle that includes: an engine; a first motor capable of inputting/outputting power; a planetary gear in which three rotation elements are connected to a rotational shaft of the first motor, an output shaft of the engine, and a drive shaft coupled to an axle such that the rotational shaft, the output shaft, and the drive shaft are aligned in this order in a collinear diagram; a second motor capable of inputting/outputting the power from/to the drive shaft; and a battery capable of transmitting electric power to/from the first motor and the second motor.
2. Description of Related Art
A nickel hydrogen storage battery including: a positive electrode that contains a positive electrode active material having nickel hydroxide, to which zinc is dissolved in a solid state and added, as a main component; a negative electrode that contains a hydrogen storage alloy containing manganese; and an alkaline electrolytic solution has conventionally been suggested (for example, see Japanese Patent Application Publication No. 2004-119271 (JP 2004-119271 A)). In this nickel hydrogen storage battery, magnesium is dissolved in nickel hydroxide of the positive electrode in the solid state, and magnesium is also dissolved in the hydrogen storage alloy of the negative electrode in the solid state. In this way, elution of zinc from nickel hydroxide of the positive electrode and elution of manganese from the hydrogen storage alloy of the negative electrode, which are associated with a lapse of a charging/discharging cycle, can be suppressed. In this way, degradation of a high-rate discharging characteristic after the lapse of the charging/discharging cycle can be suppressed.
In addition, a hybrid vehicle including: an engine; a first MG; a power split device (a planetary gear) in which a sun gear, a planetary carrier, and a ring gear are connected to a transmission shaft that is coupled to the first MG, the engine, and an axle; a second MG connected to the transmission shaft; and a power storage device for transmitting electric power to/from the first MG and the second MG has been suggested (for example, see Japanese Patent Application Publication No. 2013-6430 (JP 2013-6430 A)).
In such a hybrid vehicle, in the case where the nickel hydrogen storage battery is used as the power storage device, a conductive material is possibly eluted from the positive electrode of the battery, and deterioration of the battery is possibly promoted. In the case where a positive electrode potential of the battery is lowered to suppress the deterioration of the battery, maximum allowable electric power that can be output from the battery is limited. However, in the case where the maximum allowable electric power of the battery is limited, just as described, during a reverse travel, maximum power for the reverse travel that can be output from the second MG is reduced, and thus driving performance during the reverse travel is possibly degraded.